MUSEUM OF COMPARATIVE ZOOLOGY. 61 



Gegenbaur considers it probable that this membrane is produced by 

 the follicular epithelium, but is evidently not certain of it. He says : 

 "Es liegen hier wohl bei den Selachiern andere Verhaltnisse vor als bei 

 den Vogeln und Reptilien, und eine Dotterhaut, wie sie dort von Seite 

 des Dotters durch Umwandlung seiner peripherischen Schichte zu Stande 

 kam, kommt hier wohl nicht vor, sondern der Dotter bleibt auf dem 

 friiheren Stadium der Differenzirung bestehen, dagegen bildet sich eine 

 Hiille von aussen her, wozu wabrscheinlich die Zellen des Follikelepithels 

 das Material abscheiden, wenn man den Vorgang der Bildung jener 

 Membran nicht auf die Oberfliiche des Dotters selbst verlegen will." 



Schultz and Balfour disagree in their conclusions as to the origin of 

 the fugitive rrembranes which envelop the ovarian eggs of selachians. 

 Schultz ascribes their formation to the follicular cells ; Balfour, to the 

 ovum itself. 



Schultz ('75, pp. 574-576) claims that in Torpedo oculata the fol- 

 licular epithelium is composed of two kinds of cells : genuine granulosa 

 cells, derived from the germinal epithelium of the ovary, and, alternating 

 with them, lymphoid cells, which are derived from the stroma of the 

 sexual organ. " The cells of this follicular epithelium, especially the 

 lymphoid cells, are merged at their deeper ends into a homogeneous 

 cuticular layer (Fig. 8), and there form a structure having the morpho- 

 logical value of a chorion." This homogeneous layer at no time has a 

 morphological relation to the egg protoplasm, but retains the closest con- 

 nection with the follicular cells. On objects subjected to pressure the 

 outer margin of the homogeneous layer appears jagged like a wood-saw, 1 

 the remnants of the lymphoid cells corresponding to the teeth, in the 

 intervals between which the granulosa cells are lodged. The latter are 

 also attached, he says, to the homogeneous layer by means of proto- 

 plasmic processes, and even appear to fuse with it, but do not show any 

 differentiation within the substance of the layer. It is not possible 

 even with the highest powers to demonstrate any such structural pecu- 

 liarities (radial striation, pore-like perforations) as are met with in the 

 egg membranes of most classes of animals, even in Raja batis itself. 



" Finally, when the egg cell has reached maturity and the follicle 

 approaches the stage of rupturing, the lymphoid cells together with the 

 homogeneous layer are converted into connective issue, in the inter- 

 stices of which the granulosa cells persist, although the latter finally 

 undergo fatty degeneration. Only at a single place, corresponding to 

 the whole extent of the germinal disk, do the follicular cells and the 



1 " Gleichsam hohlsageformig [hohlzsageformig ?] gezackt." 



